1. Field of the Invention
The disclosure generally relates to a communication device, and more particularly, relates to a communication device comprising a MIMO (Multi-Input and Multi-Output) antenna system with high isolation.
2. Description of the Related Art
As people demand more and more data transmission, related communication standards are supporting higher and higher data transmission rates. For example, IEEE 802.11n can support MIMO technology to increase transmission rates. The related communication standards, such as LTE (Long Term Evolution), also support MIMO operations. As a matter of fact, it is a future trend to use multiple antennas in a mobile device. However, since multiple antennas are to be disposed in a limited space of a mobile device, the isolation between these antennas is an important factor to be considered.
Traditionally, the method for improving isolation and for reducing mutual coupling between MIMO antennas is to dispose an isolation element between two adjacent antennas, wherein the resonant frequency of the isolation element is approximately equal to that of the antennas so as to decrease the mutual coupling between the antennas. The drawbacks of the traditional method include decreased antenna efficiency and degraded radiation performance. In addition, if these antennas are operated in an LTE 700 band (from 704 MHz to 787 MHz), the isolation element is required to resonate at about 700 MHz and hence requires a large element size, which greatly increases the size of the whole antenna system. Integration of such an antenna system in the limited space inside the mobile device is a challenge for an antenna designer.
Accordingly, there is a need to provide a new communication device which performs MIMO operations without any isolation element but has good isolation. The antenna efficiency of the antenna system in the communication device should not be affected, or should even be enhanced.